The influence of dissolved organic carbon on sorption of heavy metals on urea-treated pine bark.

A previous study showed considerably higher metal adsorption by urea-treated pine bark (UTB) compared to non-treated bark (NTB) at metal adsorption from their individual relatively concentrated solutions. Comparison of the sorption characteristics of the two pine barks at low but environmentally relevant metal concentrations, and investigation of the influence of pH and dissolved organic carbon (DOC) on the sorption process are the aims of the present study. Sorption of Cu(2+), Ni(2+), Zn(2+) and Pb(2+) on pine bark of the species Pinus sylvestris was measured in multi-metal solutions in the presence and absence of DOC. In the absence of DOC, UTB gave lower residual metal concentrations (2-7 microg/l for copper, 1-5 microg/l for nickel, <0.05 microg/l for zinc and lead) in the range of initial concentrations up to 0.7 mg/l, compared to NTB (6-15 microg/l for copper, 2-24 microg/l for nickel, 2-9 microg/l for zinc, 2-3 microg/l for lead). In the presence of DOC, sorption of Zn, Ni and Pb decreased by up to 75% depending on the DOC concentration. Metal sorption on UTB is less sensitive to pH and more adsorbed metal ions are retained compared to NTB. The potential use of urea-treated bark for treatment of waste water containing DOC and low concentrations of metals is discussed.